1. Field of the Invention
This invention relates to a method and apparatus for subterranean drilling. In one aspect, this invention relates to a method and apparatus for completion of oil, gas and/or hydrothermal wells. In one aspect, this invention relates to the use of lasers for subterranean drilling, including initiation and promotion of flow of a desired resource into a wellbore, referred to herein as perforation. In one aspect, this invention relates to a method and apparatus for removal of debris produced by lasers during subterranean drilling. In yet another aspect, this invention relates to the use of extensible laser head assemblies for perforation of wellbores.
2. Description of Related Art
Once the drilling of a wellbore has been completed, fluid flow into the wellbore is initiated by perforating the wellbore casing or liner. Such perforations are normally created using bullets or shaped charges for establishing flow of oil or gas from the geologic formations surrounding the wellbore into the wellbore. However, there are numerous problems with this approach. For example, the melt from shaped charges or debris from the bullet impact usually reduces the permeability of the producing formations resulting in a substantial reduction in production rate. In addition, these techniques involve the transportation and handling of high power explosives and are causes of serious safety and security concerns. Moreover, the impact of the bullet into the formation also produces fine grains that can plug the pore throat, thereby reducing the production rate. And, finally, the depth of the perforations into the formations is limited to a few inches.
In an attempt to address certain of these issues, U.S. Pat. No. 6,888,097 to Batarseh teaches the use of laser energy for creating the perforations. More particularly, the '097 patent teaches a high power laser disposed above ground coupled with a fiber optic cable that transmits laser energy downhole. On the end of the fiber optic cable is a mechanical means that allows for precise control over the motion and location of the fiber optic cable. In accordance with one embodiment, a plurality of spherical wheels or other suitable means of locomotion mounted on retractable mechanical arms are connected with the fiber optic cable. After the laser penetrates the wellbore casing and cement, the fiber optic cable can be transported through each medium into the actual perforation, allowing for the creation of a much deeper perforation. The apparatus is capable not only of drilling deeper into the perforated opening, but also of acting upon the surface of the perforation. Different types of laser treatments can be employed to yield fully vaporized (high permeability), porous melt (moderate permeability) or sealed (impermeable) rock layers. These different treatments are required to cope with the different strengths and stabilities of the rock formations encountered. The desired results can be obtained by manipulating simple laser parameters, such as laser power and exposure time.
There are, however, certain disadvantages associated with the method and apparatus of the '097 patent and there are certain issues associated with wellbore perforation by conventional means that are not addressed by the teachings of the '097 patent. One of the disadvantages is that the method and apparatus require that the fiber optic cable be transported by the means of locomotion into the perforation to limit the distance between the fiber optic cable end and the target area to minimize attenuation of the laser energy due to the disposition of debris generated by the laser during the perforation process in the pathway of the laser beam.